Effects of Si content and free Si on oxidation behavior of Ti–Si–N coating layers

Abstract In this work, various Ti–Si–N coating layers, composites of TiN crystallites and amorphous Si 3 N 4 , where free Si existed depending on the amount of total Si content in Ti–Si–N film, were prepared on Si substrates by a d.c. reactive magnetron sputtering method in order to systematically investigate the effects of Si contents and free Si on the oxidation behavior. The oxidation process at 800 °C started by forming thin oxide layer of ternary Ti–Si–O at the interface, and the ternary Ti–Si–O layer was segregated into two phases of TiO 2 and SiO 2 . Oxidation resistance of Ti–Si–N coating layers was significantly improved with increasing Si contents, which resulted in the increase of SiO 2 amount acting as an oxygen diffusion barrier. Free Si was diffused and segregated toward surface region, while Si bonded to nitrogen in Si 3 N 4 could not. The free Si in Ti–Si–N coating layers was believed to partly contribute to the much enhanced oxidation resistance.